Alloy lead, battery grid

The above experimental results suggest that the evaluation of the corrosion resistance of lead alloys for battery grids should also account for the influence of ageing on the rate of corrosion as the lead—acid battery is a long-living product. 

Rao, P, Calcium Tin Silver Lead Based Alloys and Battery Grids and Lead Acid Batteries, U.S. Patent 5,298,350 (March 29,1994). 

Important physical characteristics of antimonial lead battery grid alloys 18/10... 

The lead-bearing components ate released from the case and other nordead-containing parts, followed by the smelting of the battery plates, and refinement to pure lead or specification alloys. The trend toward battery grid alloys having Httle or no antimony, increases the abiHty of a recovery process to produce soft lead (refined). As requited in the production of primary lead, each step in the secondary operations must meet the environmental standards for lead concentration in ait (see Air pollution Lead compounds, industrial toxicology). 

Automobile battery grids employ about 1—3 wt % antimony—lead alloys. Hybrid batteries use low (1.6—2.5 wt %) alloys for the positive grids and nonantimony alloys for the negative grids to give reduced or no water loss. The posts and straps of virtually all lead—acid batteries are made of alloys containing about 3 wt % antimony. 

Fig. 4. Grain structure of lead—2 wt % antimony alloy battery grid at a magnification of 50x (a) no nucleants (b) containing 0.025 wt % selenium as a grain...

Lead alloys containing 0.09—0.15 wt % calcium and 0.015—0.03 wt % aluminum are used for the negative battery grids of virtually all lead—acid batteries in the United States and are also used in Japan, Canada, and Europe. If the molten alloy is held at too low a temperature, the aluminum precipitates from solution, rises to the surface of the molten alloy as finely divided aluminum particles, and enters the dross layer atop the melt. 

Lead—Calcium-Tin Alloys. Tin additions to lead—calcium and lead—calcium—aluminum alloys enhances the mechanical (8) and electrochemical properties (12). Tin additions reduce the rate of aging compared to lead—calcium binary alloys. The positive grid alloys for maintenance-free lead—calcium batteries contain 0.3—1.2 wt % tin and also aluminum. 

Wrought lead—calcium—tin alloys contain more tin, have higher mechanical strength, exhibit greater stabiUty, and are more creep resistant than the cast alloys. RoUed lead—calcium—tin alloy strip is used to produce automotive battery grids in a continuous process (13). Table 5 Hsts the mechanical properties of roUed lead—calcium—tin alloys, compared with lead—copper and roUed lead—antimony (6 wt %) alloys. 

Selenium acts as a grain refiner in lead antimony alloys (114,115). The addition of 0.02% Se to a 2.5% antimonial lead alloy yields a sound casting having a fine-grain stmcture. Battery grids produced from this alloy permit the manufacture of low maintenance and maintenance-free lead—acid batteries with an insignificant loss of electrolyte and good performance stability. 

Trace quantities of arsenic are added to lead-antimony grid alloys used ia lead—acid batteries (18) (see Batteries, lead acid). The addition of arsenic permits the use of a lower antimony content, thus minimising the self-discharging characteristics of the batteries that result from higher antimony concentrations. No significant loss ia hardness and casting characteristics of the grid alloy is observed (19,20). 

The proper selection of the lead alloy depends on the intended use and the economics of the lead—acid battery appHcation. The metallurgical and electrochemical aspects of the lead are discussed in the Hterature in a comprehensive manner (81,85—87) as are trends of lead alloy use for manufacture of battery grids (88). 

A simple, rapid and seleetive eleetroehemieal method is proposed as a novel and powerful analytieal teehnique for the solid phase determination of less than 4% antimony in lead-antimony alloys without any separation and ehemieal pretreatment. The proposed method is based on the surfaee antimony oxidation of Pb/Sb alloy to Sb(III) at the thin oxide layer of PbSOyPbO that is formed by oxidation of Pb and using linear sweep voltammetrie (LSV) teehnique. Determination was earried out in eoneentrate H SO solution. The influenee of reagent eoneentration and variable parameters was studied. The method has deteetion limit of 0.056% and maximum relative standard deviation of 4.26%. This method was applied for the determination of Sb in lead/aeid battery grids satisfaetory. 

Antimony alloys have many commercial applications. The metal makes its alloys hard and stiff and imparts resistance to corrosion. Such alloys are used in battery grids and parts, tank linings, pipes and pumps. The lead plates in the lead storage batteries constitute 94% lead and 6% antimony. Babbit metal, an alloy of antimony, tin, and copper is used to make antifriction machine bearings. Alloys made from very high purity grade antimony with indium, gallium and bismuth are used as infrared detectors, diodes, hall effect devices and thermoelectric coolers. 

The major uses are in metallurgy, primarily as an additive to lead, copper, brass and many lead-base bearing alloys to improve their mechanical and thermal properties. Small amounts are added to lead in the manufacture of lead shot to improve its sphericity also added to lead-base cable sheathing and battery grid metal to improve hardness. Addition of very small quantities to copper enhances the corrosion resistance. It prevents cracking in brass. 

The applications of arsenic as a metal are quite limited. Meialluigically, it is used mainly as an additive. The addition of from to 2% of arsenic improves the sphericity of lead shot. Arsenic in small quantities improves the properties of lead-base bearing alloys for high-temperature operation. Improvements m hardness of lead-base battery grid metal and cable-sheathing alloys can be obtained by slight additions of arsenic. Very small additions (0.02 - 0.05%) of arsenic to brass reduce dezincdfication. 

Hardening mechanism in lead-calcium alloys. Lead-calcium alloys harden extremely rapidly 80% of the ultimate strength is reached in one day, and virtually full ageing in seven days. Such rapid hardening enhances grid handling and battery production. The rapid hardening was a benefit to VRLA batteries. 

Even higher tin contents (up to 2wt.%) have been reported [89] to provide reduction in the rate of corrosion and growth of positive lead-calcium grids in VRLA batteries employed in standby service at elevated temperatures. The beneficial effects of high tin on positive-grid corrosion in VRLA batteries have recently been confirmed [90]. It is proposed that the improved corrosion resistance is due to the large number of fine precipitate particles and better accommodation of the stresses of corrosion by the high mechanical properties of the alloys. 

The grid metallics should be stored and recovered separately from the battery paste so that metals from the alloys in the battery grids do not contaminate the relatively pure lead paste, which is ideal for producing soft lead. Alloys used to manufacture VRLA batteries do not contain either antimony or arsenic, and this means that the potential hazard of stibine (antimony hydride, SbHs) and arsine (arsenic hydride, AsHs) formation during the storage of the metallics is removed. Many automotive batteries with antimonial and arsenical alloys are still in use. 

The first grid alloys used were lead alloys with 11% antimony content called hard lead . These alloys were replaced with low-antimony lead alloys with additions of Sn, As and Ag. Later, battery grid manufacturers switched to lead—calcium and lead—calcium—tin alloys. 

Figure 4.1 presents schematically the basic properties of lead alloys which are essential for their applicability for casting battery grids. These alloy characteristics and their influence on battery performance parameters will be discussed in more detail in this chapter. 

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